I don’t think there is a way to use Ruby on your Webflow projects. Since Bourbon seems to be a SASS toolkit however you could just build your requirements locally if you have the option of hosting external assets somewhere:
Make sure you have Ruby installed on your local machine; install Bourbon; create a SASS file and import the bourbon styles using the line you quoted, add any styles you want to use the bourbon toolkit and use a tool of your liking to build the SASS down to a plain CSS file, which you can then put on your hosting server.
Inserting a <link rel="stylesheet" href="your-css-file's-url" /> in the header custom code will then load the additional styles on your Webflow site.